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What's one of the best-kept secrets for healthy hair? Is it the latest exotic potion from Europe? An exclusive Hollywood salon conditioner? You might be surprised to learn that it's a balanced diet! Experts agree that a healthy diet with the right mix of protein, iron, and other nutrients can help improve the health, look, and feel of your hair.

"To a doctor," says Amy McMichael, MD, "healthy hair is hair that's growing appropriately out of every follicle, not easily broken, and connected to a healthy scalp. To a patient, it's hair that's as long and full as you'd like it to be. It's bouncy, shiny, and manageable." McMichael is the director of the Hair Disorder Clinic at Wake Forest Baptist Health in Winston-Salem, N.C. She tells WebMD that a balanced diet can give your hair all the nutrients it needs to satisfy both definitions for healthy hair.

Healthy Hair: Protein Is Important

Your hair needs the same well-rounded diet that provides all the recommended vitamins, minerals, and other nutrients required for good health in the rest of your body. But it doesn't mean that when it comes to hair, all nutrients are equal, especially when it comes to protein.

A strand of hair is composed of mostly protein, which means your hair needs protein to grow. "Some people mistakenly take extra calcium," says dermatologist Paradi Mirmirani, MD, of the Permanente Medical Group in Vallejo, Calif., and a member of the North American Hair Research Society. "But hair and nails are both protein fibers."

At any given time, about 90% of your hair is in the growing phase. For each individual hair, this growing phase lasts 2 to 3 years. At the end of that time, hairs enter a resting phase that lasts about 3 months before they are shed and replaced by new hair. If you don't get enough protein in your diet, a disproportionate number of hairs may go into the resting phase.

On a normal scalp, there are about 120,000-150,000 strands of hair, and about 50 to 100 strands of that are shed each day. Most people don't even notice that small amount. But if an unusually large number of hairs enter the resting phase at the same time, hair loss can become noticeable, even alarming.

The good news is that the problems caused by not getting enough protein can be reversed. By restoring protein to your diet, whether it comes from plants, such as beans and other legumes, whole grains, and soy, or meat from animal sources, you can restore the normal hair cycle and stop the abnormal hair loss.

Iron and Other Nutrients

Protein isn't the only nutrient needed to maintain healthy hair. Christine Gerbstadt, MD, RD, spokesperson for the American Dietetic Association, tells WebMD that you also need iron, vitamin E, and trace minerals, such as selenium, copper, and magnesium to help keep your hair in good shape. "These are all involved in the production of the various proteins that make up your hair."

Iron may be the most problematic of these nutrients to get in effective amounts, especially for women and vegetarians. Not getting enough iron, like not getting enough protein, can cause hair loss.

"The best source of iron in your diet is meat," Gerbstadt says. At the top of the source list for iron are clams, oysters, and organ meat. "But there are problems with eating a lot of organ meat," Gerbstadt tells WebMD. "Lean meat, though -- pork, beef, and fish -- are all good sources."

Good vegetarian sources of iron include fortified cereals, soybeans, pumpkin seeds, white beans, lentils, and spinach. The problem with iron from non-animal sources is that the body absorbs iron less efficiently from plants. "It's possible to eat a vegetarian diet paying attention to iron and still not get enough," Gerbstadt says.

Gerbstadt suggests talking with your doctor about your diet and asking your doctor to test the level of iron in your body. With a simple blood test, your doctor can determine whether or not you should consider taking an iron supplement.

Vitamin D and Your Hair

Another potentially important nutrient is vitamin D. Mirmirani says that though the evidence still isn't clear, some studies suggest that vitamin D may play a role in the hair cycle. "We can get vitamin D from the sun," Mirmirani says. "But dermatologists don't recommend a lot of sun exposure."

Dietary sources of vitamin D include fortified foods such as milk, orange juice, and cereals. But, Mirmirani says, according to some studies, many Americans aren't getting enough vitamin D. "And the actual recommended dosage is controversial," she says. As with iron, she recommends talking with your doctor about your vitamin D needs and whether or not you should take a supplement.

Are Hair Supplements Necessary?

Carolyn Jacob, MD, founder and medical director of Chicago Cosmetic Surgery and Dermatology, tells WebMD, "Any vitamin deficiency will cause hair loss. All the vitamins are important -- B, C, E." But that doesn't mean, as she and other experts point out, that you need to buy special supplements for your hair.

"The best source for the nutrients you need," Jacob says, "is a true, well-balanced diet." If you are going to take an over-the-counter supplement, Jacob says, talk with your doctor or nutritionist to make sure you're "getting a high-grade women's multivitamin that will ensure you get what you need."

Mirmirani says she is often asked about adding zinc or biotin supplements to a diet. "I don't check the zinc or biotin levels in patients," she says. "It's very hard in an American diet for those things to become deficient. And there hasn't been any good evidence that taking zinc or biotin supplements actually offers any benefits for hair."

She goes on to say that taking extra biotin probably won't hurt. "But it's not clear it does much good, either." You need to weigh the monetary cost against what health benefit you think you might get.

Hair Health and Weight Loss Diets

According to McMichael, weight loss, especially rapid weight loss from a restrictive diet, can cause major hair loss. "For instance, when the Atkins diet came out, I saw a tremendous number of women who were complaining about hair loss."

McMichael says, "Women on a very strict calorie-deprived diet will lose weight very quickly. But it's hard to ensure they get the nutrients they need. "In addition, weight loss causes physiological stress, which also contributes to hair loss."Even if you lose weight very slowly on a doctor-approved program, you can still have associated hair loss."

Shedding hair after a weight loss of 15 pounds or more is common. The hair loss is reversible, McMichael says, and in otherwise healthy individuals, hair will come back after weight stabilizes.

Gerbstadt says it's important to be patient and remember you can't do both -- lose weight and nurture your hair -- at the same time. "Master hairdressers," she says, "know without being told when their clients are dieting -- just from the changes in the hair."

Staying Balanced

Gerbstadt says the important thing to do is remember that "balance" is the key word to keep in mind. A healthy diet supplemented with a good daily multivitamin is the best diet plan for healthy hair, Gerber advises.